Chlorine dioxide is a potent and useful oxidizing agent that may be used as a disinfectant, biocide, sanitizer, etc. in processes such as water treatment, cleaning, bleaching, etc. Chlorine dioxide is effective against a wide variety of pathogens.
While not wishing to be constrained by any single reaction pathway, one known reaction of sodium chlorite (NaClO2) with hydrochloric acid (HCl) and sodium hypochlorite (NaOCl) produces chlorine dioxide (ClO2), sodium chloride (NaCl), and water (H2O), as follows:2NaClO2+2HCl+NaOCl→2ClO2+3NaCl+H2O
In addition, while not wishing to be constrained by any single reaction pathway, one known reaction of sodium chlorite with hydrochloric acid produces chlorine dioxide, sodium chloride, and water, as follows:5NaClO2+4HCl→4ClO2+5NaCl+2H2O
Furthermore, while not wishing to be constrained by any single reaction pathway, one known reaction of sodium chlorite with hypochlorous acid (HOCl) produces chlorine dioxide, sodium chloride, and sodium hydroxide, as follows:2NaClO2+HOCl→2ClO2+NaCl+NaOHAlso, while not wishing to be constrained by any single reaction pathway, one known reaction of sodium chlorite with chlorine gas (Cl2) produces chlorine dioxide and sodium chloride, as follows:2NaClO2+Cl2→2ClO2+2NaCl
Chlorine dioxide may exist as a greenish yellow gas at room temperature and possess a characteristic chlorine-like odor. While chlorine dioxide is highly soluble in water. Chlorine dioxide is also highly volatile and may readily migrate out of solution and into the gas phase. Moreover, chlorine dioxide is subject to photochemical decomposition and to chemical decomposition through disproportionation. Therefore, chlorine dioxide solutions may have a relatively short shelf life. When chlorine dioxide is in the gas phase at concentrations exceeding 30% volume in air, at standard temperature and pressure, chlorine dioxide may explosively decompose into chlorine and oxygen. Furthermore, chlorine dioxide is poisonous and is a severe respiratory and eye irritant.
To compensate for the above-noted issues, chlorine dioxide has been produced from relatively stable precursor species at the end use facilities, which has required either a generator to produce chlorine dioxide solutions or a relatively long reaction time to produce chlorine dioxide from generatorless systems.
The generator based systems may use a mechanical or electrical element to facilitate or control the rate of production of chlorine dioxide. Generators may be chemical or electrochemical. Electrochemical generators typically fall into two categories, those that oxidize a chlorite ion and those that reduce a chlorate ion. Chemical based generators typically generate chlorine dioxide by blending high concentrations of sodium chlorite and hydrochloric acid or sulfuric acid. Generator based systems produce relatively high concentrations of chlorine dioxide which may then be diluted to provide solutions including chlorine dioxide at concentrations that are suitable for use. The safety concerns associated with concentrated solutions of chlorine dioxide are well known. Most generators incorporate elaborate safety systems in an attempt to reduce the risk associated with producing, storing and handling these highly concentrated solutions, contributing significantly to the overall cost. The total cost of these generators, including operation and maintenance costs, have limited their application.
Generatorless systems for producing chlorine dioxide are known, however these systems generally require long reaction times to produce solutions of chlorine dioxide. A disadvantage of long reaction times is the risk that a user will not allow adequate formation of chlorine dioxide before using a solution, which results in ineffective microbial kills. Another disadvantage is that the long reaction time prevents quick use.
In addition, a generatorless system may include adding a high concentration of sodium chlorite to an acid solution in a bucket, waiting for the reaction to occur, and adding water to dilute the chlorine dioxide. This procedure can be very dangerous and pose health risks due to the very high concentrations of chlorine dioxide that are produced by the reaction.
As with the concentrated chlorine dioxide solutions produced by the generators, the solutions produced in generatorless systems may require dilution in order to provide a solution having a chlorine dioxide concentration that is suitable for use. The time, safety, and complexity constraints, e.g., the requirement for further dilution processing equipment and control equipment, have limited the application of these systems.